Blade fixation for ankle fusion and arthroplasty

ABSTRACT

Systems for lower extremity fusion and arthroplasty include fusion spacers, bone plates, and articular prostheses fixed to bone by blade anchors. Examples are shown for anterior, lateral, and medial approaches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of:

U.S. Application No. 61/589,721, filed Jan. 23, 2012, entitled BLADEFIXATION FOR ANKLE FUSION AND ARTHROPASTY.

The above-referenced document is hereby incorporated by reference in itsentirety.

This application incorporates by reference the following application inits entirety: U.S. patent application Ser. No. 12/640,892, filed Dec.17, 2009, entitled INTERVERTEBRAL IMPLANT WITH INTEGRATED FIXATION,which is pending.

BACKGROUND

Ankle fusion rates are negatively affected, and ankle arthroplastyrevision rates increase, due to the loads, stresses, high range ofmotion, and complex motion of the ankle joint. Secure fixation of theankle during fusion and secure fixation of the ankle arthroplastycomponents contribute to the success of the procedure by preventingpost-operative loosening or subsidence of components. Leg-lengthdiscrepancies are also common pre- and post-operatively, thus there is aneed to restore leg length with a fusion or arthroplasty implant. Thereis also a need for easy, repeatable, secure ankle fixation devices andmethods.

SUMMARY

In an aspect of the technology, a system includes a first implant bodywith a first bone-contacting surface and a first channel on the firstbone-contacting surface; and a first anchor coupled to the first implantbody, the first anchor including a first bone fixation feature carriedoutside the first implant body, a first connecting feature fixed in thefirst channel, and a first intermediate portion connecting the firstbone fixation feature to the first connecting feature, wherein the firstintermediate portion extends through the first bone-contacting surface;wherein the first channel and the first connecting feature havecomplementary interconnecting shapes, wherein the first connectingfeature slidingly engages the first channel to couple the first anchorto the first implant body.

In an embodiment, the system includes a second anchor like the firstanchor; wherein the second anchor is coupled to the first implant body.

In another embodiment, the second anchor is coupled to the firstchannel.

In yet another embodiment, the second anchor is coupled to a secondchannel on a second bone-contacting surface of the body.

In yet another embodiment, the second anchor is coupled to a secondchannel on the first bone-contacting surface.

In yet another embodiment, the system includes a third anchor like thefirst anchor; wherein the third anchor is coupled to the first implantbody.

In yet another embodiment, the third anchor is coupled to a thirdchannel on a second bone-contacting surface of the body.

In yet another embodiment, the system includes a fourth anchor like thefirst anchor; wherein the fourth anchor is coupled to the first implantbody.

In yet another embodiment, the fourth anchor is coupled to a fourthchannel on the second bone-contacting surface of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

While exemplary embodiments of the present technology have been shownand described in detail below, it will be clear to the person skilled inthe art that changes and modifications may be made without departingfrom its scope. As such, that which is set forth in the followingdescription and accompanying drawings is offered by way of illustrationonly and not as a limitation. The actual scope of the invention isintended to be defined by the following claims, along with the fullrange of equivalents to which such claims are entitled.

In addition, one of ordinary skill in the art will appreciate uponreading and understanding this disclosure that other variations for thetechnology described herein can be included within the scope of thepresent technology.

In the following Detailed Description, various features are groupedtogether in several embodiments for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that exemplary embodiments of the technologyrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus, the followingclaims are hereby incorporated into the Detailed Description, with eachclaim standing on its own as a separate embodiment.

Identical reference numerals do not necessarily indicate an identicalstructure. Rather, the same reference numeral may be used to indicate asimilar feature or a feature with similar functionality. Not everyfeature of each embodiment is labeled in every figure in which thatembodiment appears, in order to keep the figures clear. Similarreference numbers (e.g., those that are identical except for the firstnumeral) are used to indicate similar features in different embodiments.

FIG. 1 is a front view of a left tibiotalar joint with a fusion spacersecured within the joint;

FIG. 2 is a front view of the fusion spacer of FIG. 1;

FIG. 3 is a front view of another fusion spacer;

FIG. 4 is a side view of the fusion spacer of FIG. 1;

FIG. 5 is a side view of a left tibiotalar joint with yet another fusionspacer secured within the joint;

FIG. 6 is a front view of a set of anchors, each having a differentcross sectional shape;

FIG. 7 is a side view of a left tibiotalar joint with a fusion platesecured across the joint;

FIG. 8 is a front view of a left tibiotalar joint with another fusionplate secured across the joint;

FIG. 9 is an exploded side view of an ankle arthroplasty device;

FIG. 10 is an exploded front view of the ankle arthroplasty device ofFIG. 9;

FIG. 11 is an isometric view of a body of the fusion spacer of FIG. 1;

FIG. 12 is a front view of yet another fusion spacer;

FIG. 13 is a front view of yet another fusion spacer;

FIG. 14 is a front view of yet another fusion spacer;

FIG. 15 is a side view of yet another fusion spacer;

FIG. 16 is a side view of yet another fusion spacer;

FIG. 17 is a side view of yet another fusion spacer;

FIG. 18 is a side view of the fusion spacer of FIG. 5;

FIG. 19 is a side view of yet another fusion spacer;

FIG. 20 is a side view of yet another fusion spacer; and

FIG. 21 is a front view of the fusion spacer of FIG. 5.

DETAILED DESCRIPTION

Standard medical planes of reference and descriptive terminology areemployed in this specification. A sagittal plane divides a body intoright and left portions. A mid-sagittal plane divides the body intoequal right and left halves. A coronal plane divides a body intoanterior and posterior portions. A transverse plane divides a body intosuperior and inferior portions. Anterior means toward the front of thebody. Posterior means toward the back of the body. Superior means towardthe head. Inferior means toward the feet. Medial means toward themidline of the body. Lateral means away from the midline of the body.Axial means toward a central axis of the body. Abaxial means away from acentral axis of the body.

The present technology may be employed in a fusion spacer withintegrated blade anchor fixation. The spacer includes a body disposedbetween at least two bones or bone portions. The body includes channelsto accept one or more fixation blades, or anchors, per bone/implantinterface. In other words, the body includes at least one channel oneach bone-contacting surface, and may include more than one channel perbone-contacting surface. Each channel may accept one or more fixationblade anchors. The body may also include at least one hole orfenestration that extends between bone-contacting surfaces. The hole maybe centrally located. The hole may contain bone fusion material, such asautograft bone, allograft bone, demineralized bone matrix (DBM),osteoconductive, or osteoinductive agents, among others. Each fixationblade, or anchor, may slide into a corresponding channel, and at thesame time, into an adjacent portion of bone. The fixation blade, oranchor, may be impacted into the channel and bone portion. The fixationblade anchor may lock to the fusion spacer upon insertion so that theanchor may not migrate or be unintentionally removed from the fusionspacer. The anchor and/or fusion spacer may include integrated lockingfeatures or mechanisms so that locking occurs automatically as theanchor reaches full insertion. As the fixation blade, or anchor,advances into the channel and bone portion, the body and bone portionmay be urged into compression. Additional fixation devices may also beincluded, such as pegs, stems, keels, screws, and the like.

FIGS. 1-2, 4, and 11 illustrate an example of a fusion spacer for ananterior approach to an ankle joint. Fusion spacer 10 includes a body 12that may be disposed between a tibia 99 and a talus 97 as shown in FIG.1 in an anterior view of an ankle joint. This example may be implantedthrough an anterior approach, although other examples may be implantedthrough other approaches. The body 12 includes two bone-contactingsurfaces 6, 8 and a perimeter surface 4 extending around the bodybetween the bone-contacting surfaces. Surface 6 is a tibia-contactingsurface and surface 8 is a talus-contacting surface. Surface 6 may bestraight across in an anterior view (FIGS. 1-2) and may be convex in alateral view (FIGS. 4 and 11) in order to approximate a distal articularsurface of a tibia. Surface 8 may be straight across in an anterior view(FIGS. 1-2) and may be concave in a lateral view (FIGS. 4 and 11) inorder to approximate a proximal articular surface of a talus. Surfaces6, 8 may be sections of cylinders, or semi-cylindrical. In otherexamples, the bone-contacting surfaces may be shaped differently to suitthe particular implantation site. The body 12 may also include at leastone hole 11 or fenestration that extends between bone-contactingsurfaces. The hole 11 may be centrally located or off-center. The hole11 may contain bone fusion material, such as autograft bone, allograftbone, demineralized bone matrix (DBM), osteoconductive, orosteoinductive agents, among others. The body may include at least onechannel 14 on each bone-contacting surface 6, 8. The body 12 may includea plurality of channels 14 that accept at least one fixation bladeanchor 16 for each bone-implant interface. Each channel 14 may includean undercut keyway which is complementary to a portion of the bladeanchor 16. The channels 14 in this example are oriented to extend in ananterior-posterior direction when the fusion spacer 10 is implanted.

The blade anchors 16 may include a connecting feature 18, such as aknob, hook, key, tee, dovetail, rail, or other feature designed forcomplementary interconnecting fit with the channel 14 on the spacer body12. The blade anchors 16 may be substantially T-shaped, and include anelongated intermediate portion 20 and a bone fixation feature 22.

The anchors in the present disclosure may share some or all of thefeatures of the anchors disclosed in pending U.S. patent applicationSer. No. 12/640,892 to Bae, et al., which is incorporated by referenceherein in its entirety.

In use, the distal tibia and proximal talus may be exposed from ananterior approach, and the bones prepared with cutting instruments,jigs, and other tools to remove damaged, diseased, or otherwiseundesirable articular cartilage and/or bone. This bone preparationestablishes resection surfaces on the tibia and talus, which may begeometric approximations or idealizations of the removed natural bonesurfaces, or undamaged natural bone surfaces. The resection surfaces mayalso match or complement the corresponding bone-facing surfaces on thespacer body 12. In this example, a distal tibial resection surface (notshown) may be straight across in an anterior view and convex in alateral view. A proximal talar resection surface (not shown) may bestraight across in an anterior view and concave in a lateral view. Trialbodies may be inserted into the tibiotalar joint space from an anteriordirection to determine an appropriate length, width, thickness, height,and/or varus/valgus tilt for the spacer body 12. The appropriately sizedspacer body 12 may then be selected from a kit or set of spacer bodiesand inserted into the joint space from an anterior direction. Theanchors 16 may then be aligned with the corresponding channels 14 andslidingly inserted into the channels and adjacent bone portions from ananterior direction. Additional tools may be used in this step tofacilitate anchor alignment and insertion.

Referring to FIG. 4, the connecting feature 18, or rail, may beinterrupted or intermittent along the length of the blade anchor 16, orthe rail may be continuous.

FIG. 6 illustrates some alternative configurations for thebone-anchoring blades 16, as viewed from an end, or in other words,along an insertion direction. Each of the alternative anchorconfigurations 216, 316, etc. is distinguished by a bone fixationfeature 222, 322, etc. and a connection feature 218, 318, etc. coupledtogether by an intermediate portion 220, 320, etc. The intermediateportion is narrower than either the bone fixation feature or theconnection feature. In other words, the bone fixation feature and theconnection feature are each wider than the intermediate portion. Thisarrangement, in the illustrated examples and others like them, enablesthe anchor 16 (specifically the intermediate portion) to perform as atension-compression member to transfer tensile and compressive loadsbetween the body and the adjacent bone portion.

FIG. 3 illustrates another example of a fusion spacer 110 for anteriorinsertion. Spacer 110 includes a body 112 with two channels 114 on eachbone-contacting surface 106, 108. In this example, the channels 114alternate between surface 6 and surface 8 across a width of the body112. Other characteristics of spacer 110 may be similar to, or identicalto, those of spacer 10, including the orientation of the channels 114.

FIGS. 12-14 show yet more examples of fusion spacers for anteriorapproach to the ankle joint. FIG. 12 shows a fusion spacer 1010 with abody 1012 having channels 1014 directly opposite each other. FIG. 13also shows a fusion spacer 310 with a body 312 having channels 314directly opposite each other. This example includes anchor 316. FIG. 14shows a spacer 410 with a body 412 and anchor 316. Body 412 may beidentical to body 12.

FIGS. 5, 18, and 21 illustrate yet another example of a fusion spacer210, this time for lateral or medial insertion. The spacer body 212 mayresemble spacer 12, at least with regards to the bone-contactingsurfaces 6, 8; the perimeter surface 4; and optionally the fenestration11. However, in this example, channels 214 extend in a medial-lateraldirection when the fusion spacer 210 is implanted. Like spacer 110,spacer 210 includes two channels on each bone-contacting surface, thechannels alternating between the bone-contacting surfaces across a widthof the body 212.

FIGS. 15-17 and 19-20 show yet more examples of fusion spacers forlateral or medial approach to the ankle joint. FIG. 15 shows a fusionspacer 510 with a body 512 carrying one anchor 16 on eachbone-contacting surface 506, 508. FIG. 16 shows a fusion spacer 610 witha body 612 carrying one anchor 16 centrally located on bone-contactingsurface 606 and two anchors 16 bilaterally offset from center ofbone-contacting surface 608. FIG. 17 shows a fusion spacer 710 with anopposite configuration, in which body 712 carries one anchor 16centrally located on bone-contacting surface 708 and two anchors 16bilaterally offset from center of bone-contacting surface 706. FIG. 19shows a fusion spacer 810 with a body 812 carrying two anchors 16 widelybilaterally offset from center of bone-contacting surface 806 and twoanchors narrowly bilaterally offset from center of bone-contactingsurface 808. FIG. 20 shows a fusion spacer 910 with an oppositeconfiguration, in which body 912 carries carrying two anchors 16 widelybilaterally offset from center of bone-contacting surface 908 and twoanchors narrowly bilaterally offset from center of bone-contactingsurface 906. Other arrangements are contemplated, both symmetric andasymmetric.

The fusion spacers disclosed herein may be adapted for use in midfootand/or forefoot fusion procedures, such as tarsometatarsal joint fusion,hallucal fracture fusion, and the like.

The present technology may be employed in a bone plate with integratedblade anchor fixation. The plate may extend across at least two bones orbone portions. For example, the plate may extend across two bones and ajoint therebetween, or between two bone fragments and a fracture orintentional cut therebetween. The plate includes channels to accept oneor more fixation blades, or anchors, per bone/implant interface. Inother words, the plate includes at least one channel for each bone orbone fragment to be fixed to the plate, and may include more than onechannel for each bone or bone fragment to be fixed to the plate. Thebone plate may be said to have a separate bone-contacting surface, area,or region for each bone or bone fragment to be fixed to the plate. Eachchannel may accept one or more fixation blade anchors. Each fixationblade, or anchor, may slide into a corresponding channel, and at thesame time, into an adjacent portion of bone. The fixation blade may beimpacted into the channel and bone portion. The fixation blade anchormay lock to the bone plate upon insertion so that the anchor may notmigrate or be unintentionally removed from the bone plate. The anchorand/or bone plate may include integrated locking features or mechanismsso that locking occurs automatically as the anchor reaches fullinsertion. As the fixation blade advances into the channel and boneportion, the plate and bone portion may be urged into compression.Additional fixation devices may also be included, such as pegs, stems,keels, screws, and the like.

FIG. 7 illustrates an example of a bone plate system 30 for anteriorapplication across an ankle joint for fusion. Bone plate system 30includes a plate body 32 that extends anteriorly across a distal portionof a tibia and a proximal portion of a talus with a plurality ofchannels 34 configured to receive one or more fixation blade anchors 36.The channels 34, blade anchors 36, and their configuration on the platebody 32 may be similar to those described above with regard to FIGS. 1-6and 11-20. However, this example provides an opportunity to mention thatany of the anchors disclosed herein may have different heights, or depthof penetration into an adjacent bone portion. Any of the blade anchorshapes or sizes disclosed herein may be used. The plate body 32 carriesthree anchors 34, the outermost anchors penetrating deeply into adjacentbone and the middle one penetrating relatively shallowly.

The fusion plate body 32 may also include at least one aperture toprovide for bone fusion material. The aperture may be located anywherealong the plate body 32. For example, an aperture may be adjacent to achannel 34 or between two channels.

In use, the distal tibia and proximal talus may be exposed from ananterior approach. Optionally, the bones may be prepared with cuttinginstruments, jigs, and other tools to remove damaged, diseased, orotherwise undesirable periosteum, articular cartilage, and/or bone. Thisbone preparation establishes resection surfaces on the tibia and talus,which may be geometric approximations or idealizations of the removednatural bone surfaces, or undamaged natural bone surfaces. The resectionsurfaces may also match or complement the corresponding bone-facingsurfaces on the plate body 32. In this example, however, extensive bonepreparation is not shown. Trial plate bodies may be applied to theexposed tibiotalar region from an anterior direction to determine anappropriate length, width, thickness, height, and/or curvature for theplate body 32. Measuring instruments may be used instead of trials. Theappropriately sized plate body 32 may then be selected from a kit or setof plate bodies and applied to the exposed tibiotalar region from ananterior direction. The anchors 36 may then be aligned with thecorresponding channels 34 and inserted into the channels and adjacentbone portions from a lateral or medial direction. Additional tools maybe used in this step to facilitate anchor alignment and insertion. Inanother example, the channels 34 may be oriented in ananterior-posterior direction and anchors 36 may be inserted along ananterior or posterior direction.

FIG. 8 illustrates another example of a bone plate system 130, this timefor lateral or medial application across an ankle joint for fusion. Theplate body 132 may at least partially resemble plate body 32. However,in this example, channels 134 extend in an anterior-posterior directionwhen the bone plate system 130 is implanted. This example furtherillustrates the anchors 136 having different depths of penetration intoadjacent bone, or otherwise different lengths of protrusion from theplate body 132. The distal most anchor in this example has the greatestpenetration, the proximal most two anchors have the least penetration,and the second from distal most anchor has an intermediate depth ofpenetration. In another example, the channels 134 may be oriented in amedial-lateral direction and anchors 136 may be inserted along a lateralor medial direction. When applied laterally, the tibia, talus, and/orfibula each may receive at least one blade anchor.

The bone plates disclosed herein may be adapted for use in midfootand/or forefoot fusion procedures, such as fracture fixation, openingand/or closing wedge osteotomy fixation, joint fusion, and the like.

The present technology may be employed in an arthroplasty device withintegrated blade anchor fixation. The arthroplasty device, orprosthesis, may include first and second endplates, or bone-contactingcomponents, and an articular core disposed between the bone-contactingcomponents. Each bone-contacting component includes at least one channelon each bone-contacting surface to accept one or more fixation blades,or anchors. In other words, each bone-contacting component includes atleast one channel per bone/implant interface. More than one channel maybe included on each bone-contacting surface. Each channel may accept oneor more fixation blade anchors. Each fixation blade, or anchor, mayslide into a corresponding channel, and at the same time, into anadjacent portion of bone. The fixation blade may be impacted into thechannel and bone portion. The fixation blade anchor may lock to thebone-contacting component upon insertion so that the anchor may notmigrate or be unintentionally removed from the bone-contactingcomponent. The anchor and/or bone-contacting component may includeintegrated locking features or mechanisms so that locking occursautomatically as the anchor reaches full insertion. As the fixationblade advances into the channel and bone portion, the bone-contactingcomponent and bone portion may be urged into compression. Additionalfixation devices may also be included, such as pegs, stems, keels,screws, and the like.

As illustrated in FIGS. 9 and 10, an ankle arthroplasty prosthesis 41includes a tibial endplate 40, an articulating core 42, and a talarendplate 44. Similar to the previously described examples, the tibialendplate 40 and the talar endplate 44 each may have at least one channel45 in a bone-contacting surface. Each channel 45 may be configured toaccept at least one fixation blade 46. Any of the blade anchor shapes orsizes disclosed herein may be used. The fixation blade anchors 46 may beinserted anteriorly, as shown in this example, or laterally or medially,by reorienting the channels as described above for the fusion spacersand/or bone plates. In practice, the fixation blades 46 may be impactedinto the bone, resulting in compression between the endplate and thebone to achieve good compression to achieve good short-term andlong-term fixation of the prosthesis. The surgical method may be similarto the method described above for fusion spacers.

The arthroplasty prostheses disclosed herein may be adapted for use inmidfoot and/or forefoot arthroplasty procedures, such as hallux valgus,hammertoe, and the like.

The components disclosed herein may be made from metals, polymers,ceramics, glasses, composite materials, biological materials or tissues,or other biocompatible materials. Different materials may be used forindividual components. Different materials may be combined in a singlecomponent.

It should be understood that the present system, kits, apparatuses, andmethods are not intended to be limited to the particular formsdisclosed. Rather, they are to cover all combinations, modifications,equivalents, and alternatives falling within the scope of the claims.

The claims are not to be interpreted as including means-plus- orstep-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” or “step for,”respectively.

The term “coupled” is defined as connected, although not necessarilydirectly, and not necessarily mechanically.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more” or “at leastone.” The term “about” means, in general, the stated value plus or minus5%. The use of the term “or” in the claims is used to mean “and/or”unless explicitly indicated to refer to alternatives only or thealternative are mutually exclusive, although the disclosure supports adefinition that refers to only alternatives and “and/or.”

The terms “comprise” (and any form of comprise, such as “comprises” and“comprising”), “have” (and any form of have, such as “has” and“having”), “include” (and any form of include, such as “includes” and“including”) and “contain” (and any form of contain, such as “contains”and “containing”) are open-ended linking verbs. As a result, a method ordevice that “comprises,” “has,” “includes” or “contains” one or moresteps or elements, possesses those one or more steps or elements, but isnot limited to possessing only those one or more elements. Likewise, astep of a method or an element of a device that “comprises,” “has,”“includes” or “contains” one or more features, possesses those one ormore features, but is not limited to possessing only those one or morefeatures. Furthermore, a device or structure that is configured in acertain way is configured in at least that way, but may also beconfigured in ways that are not listed.

In the foregoing Detailed Description, various features are groupedtogether in several embodiments for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the embodiments of the invention requiremore features than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive subject matter lies in less than allfeatures of a single disclosed embodiment. Thus, the following claimsare hereby incorporated into the Detailed Description, with each claimstanding on its own as a separate embodiment.

The invention claimed is:
 1. A system comprising: a first implant bodycomprising a first bone-contacting surface and a first channel on thefirst bone-contacting surface, wherein the first channel comprises afirst undercut keyway; and a first anchor coupled to the first implantbody, the first anchor comprising a first bone fixation feature carriedoutside the first implant body, a first connecting feature extendingalong a length of the first anchor and fixed in the first channel, and afirst intermediate portion connecting the first bone fixation feature tothe first connecting feature and extending through the firstbone-contacting surface, wherein the first intermediate portioncomprises a front intermediate portion and a rear intermediate portionseparate from and spaced apart from the front intermediate portion alongthe length of the first anchor, wherein the first connecting feature isinterrupted along the length of the first anchor so that the firstconnecting feature is discontinuous between the front intermediateportion and the rear intermediate portion; wherein the first channel andthe first connecting feature have complementary interconnecting shapes,wherein the first connecting feature slidingly engages the first channelto couple the first anchor to the first implant body.
 2. The system ofclaim 1, comprising: a second anchor, the second anchor comprising asecond bone fixation feature carried outside the first implant body, asecond connecting feature, and a second intermediate portion connectingthe second bone fixation feature to the second connecting feature;wherein the second anchor is coupled to the first implant body.
 3. Thesystem of claim 2, wherein the second anchor is coupled to the firstchannel, wherein the second connecting feature is fixed in the firstchannel, wherein the second intermediate portion extends through thefirst bone-contacting surface.
 4. The system of claim 2, wherein thesecond anchor is coupled to a second channel on a second bone-contactingsurface of the body, wherein the second channel comprises a secondundercut keyway, wherein the second connecting feature is fixed in thesecond channel, wherein the second intermediate portion extends throughthe second bone-contacting surface.
 5. The system of claim 2, whereinthe second anchor is coupled to a second channel on the firstbone-contacting surface, wherein the second channel comprises a secondundercut keyway, wherein the second connecting feature is fixed in thesecond channel, wherein the second intermediate portion extends throughthe first bone-contacting surface.
 6. The system of claim 2, comprising:a third anchor, the third anchor comprising a third bone fixationfeature carried outside the first implant body, a third connectingfeature, and a third intermediate portion connecting the third bonefixation feature to the third connecting feature; wherein the thirdanchor is coupled to the first implant body.
 7. The system of claim 6,wherein the third anchor is coupled to a third channel on a secondbone-contacting surface of the body, wherein the third channel comprisesa third undercut keyway, wherein the third connecting feature is fixedin the third channel, wherein the third intermediate portion extendsthrough the second bone-contacting surface.
 8. The system of claim 6,comprising: a fourth anchor, the fourth anchor comprising a fourth bonefixation feature carried outside the first implant body, a fourthconnecting feature, and a fourth intermediate portion connecting thefourth bone fixation feature to the fourth connecting feature; whereinthe fourth anchor is coupled to the first implant body.
 9. The system ofclaim 8, wherein the fourth anchor is coupled to a fourth channel on thesecond bone-contacting surface of the body, wherein the fourth channelcomprises a fourth undercut keyway, wherein the fourth connectingfeature is fixed in the fourth channel, wherein the fourth intermediateportion extends through the second bone-contacting surface.
 10. Thesystem of claim 1, wherein the first connecting feature comprises afront connecting feature and a rear connecting feature separate from andspaced apart from the front connecting feature along the length of thefirst anchor, wherein the front intermediate portion connects the firstbone fixation feature to the front connecting feature, wherein the rearintermediate portion connects the first bone fixation feature to therear connecting feature.